In electronics, an opto-coupler, also referred to as an opto-isolator, photocoupler, or optical isolator, is an optoelectronic device designed to transfer electrical signals by utilizing light waves to provide coupling with electrical isolation between its input and output. One goal of an opto-coupler is to prevent high voltages or rapidly changing voltages on one side of the circuit from damaging components or distorting transmissions on the other side.
A typical opto-coupler includes a light source, such as a Light Emitting Diode (LED), a photodetector, and an insulation medium. As the name suggests, an optical path needs to be created between the LED and photodetector via the insulation medium. This is traditionally done by using an optically-transparent material such as silicone to create the light path. The insulation medium not only acts to allow the transmission of light from the LED to the photodetector, but the insulation medium also electrically insulates the input and output sides of the circuit.
One drawback to working with currently-available transparent and electrically-insulating materials such as silicone is that when applied to the opto-coupler, the silicone is in a “liquid” state and, therefore, does not has a definite shape. Accordingly, the silicone will normally take a shape due to its inherent surface tension. Using the surface tension of the silicone to shape the insulation medium is difficult and inconsistent. This characteristic can create an issue with light coupling because the shape, density, and other characteristics of the silicone and, therefore, the optical path, will vary from one opto-coupler to the next.